Initial decoupling of !is_android and enable_extension build flags

Make the enable_extension and is_android flags independent, so
(!android) would no longer imply (!extension). This change allows
better separation of concerns and should benefit the overall
Chromium project.

Bug: 1074710

Signed-off-by: Winston Chen <winston.c1@samsung.com>
Change-Id: Ie136ce2be462bdfc7b2b40ca8ab1197ca5e35b3c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2222773


Commit-Queue: Viatcheslav Ostapenko <sl.ostapenko@samsung.com>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780832}